Testing low-loss microstrip materials with MKIDs for microwave applications

TL;DR

This paper introduces a simple, practical device using MKIDs to measure the millimeter-wavelength loss of low-loss superconducting microstrip materials, aiding future astronomical measurements.

Contribution

It proposes a novel, straightforward method for characterizing microstrip dielectric loss at 150 GHz using MKIDs integrated onto the microstrip dielectric.

Findings

Microstrip loss can be measured with a practical aluminum MKID.

The device effectively characterizes dielectric loss of microstrips.

Initial results demonstrate the method's feasibility at 150 GHz.

Abstract

Future measurements of the millimeter-wavelength sky require a low-loss superconducting microstrip, typically made from niobium and silicon-nitride, coupling the antenna to detectors. We propose a simple device for characterizing these low-loss microstrips at 150 GHz. In our device we illuminate an antenna with a thermal source and compare the measured power at 150 GHz transmitted down microstrips of different lengths. The power measurement is made using Microwave Kinetic Inductance Detectors (MKIDs) fabricated directly onto the microstrip dielectric, and comparing the measured response provides a direct measurement of the microstrip loss. Our proposed structure provides a simple device (4 layers and a DRIE etch) for characterizing the dielectric loss of various microstrip materials and substrates. We present initial results using these devices. We demonstrate that the millimeter wavelength loss of microstrip lines, a few tens of millimeters long, can be measured using a practical aluminum MKID with a black body source at a few tens of Kelvin.